What is the biggest extension allowed to a house?

Postby ojb » Sun Mar 28, 2010 9:08 am


My first post here.

Does anyone know if there are general rules for the maximum size of extension which can be made to a house with planning permission.

I seem to remember that up to 40 or 50% of the original volume of the house is allowed? Can't find anything in my local authority website & they want to charge for pre-planning advice!

Anyone, please?
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Simply Build It

Postby stoneyboy » Sun Mar 28, 2010 5:36 pm

Depends where you live and whether for example you are in a green belt, aonb, conservation area etc.
You will have to look at your local councils policy documents which should answer the question
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Postby Connell » Wed Mar 31, 2010 5:59 am


It's not based on volume as from October 2008 - it's based on circumstances as Stoneyboy points out and where the extension is to be located on the original building for instance distances from common boundaries and/or highways. A highway is not just a road but anything that you can get from a to b for example a bridleway.

The legislation is under the general permitted development order as amended 2008 - class A -

But beware Council's take different interpretations as the legislation is so new that there is no case law to rely on.

You need to submit a certificate of lawfulness to make sure the building is permitted development not requiring planning permission.
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